This invention relates generally to devices for removing tree stumps, and, more particularly, to stump grinders having a cutter wheel with peripherally mounted cutter teeth.
A number of different techniques are known for removal of tree stumps, including the use of explosives, mechanical force such as by a bulldozer, and also by comminuting or grinding the stump down to ground level and preferably below. Stump grinding has advantages over other techniques for stump removal, such as greater safety than the use of dynamite, less damage to lawns or ground surfaces surrounding the stump than with the use of bulldozers or other heavy equipment.
Numerous types of equipment for grinding stumps have been devised over the years. For example, it is known to mount stump cutter teeth on one or both faces of a cutter disc or wheel which is mounted transversely, i.e., across the longitudinal axis of a machine support frame or swing arm, with the machine moving the cutter wheel forward or backward along that axis against a portion of a stump, whereby the teeth on one face contact and grind that portion. Examples of this type of equipment are described in the following patents:
______________________________________ Patent No. Inventor Issue Date ______________________________________ 2,887,134 Bartlett May 19, 1959 3,911,979 Rousseau Oct. 14, 1975 4,681,145 York Jul. 21, 1987 ______________________________________
With stumps that are wider than the cutter wheel, multiple passes through the stump are required, and on each pass this type of machine typically produces a semicircular trough matching the wheel shape. A common pattern involves grinding down to ground level on one side of a stump, repeating the process on the other side, and then grinding the remaining central portion of the stump. The remaining portion is V-shaped as viewed from above, and it thereby causes an uneven load on the engine driving the cutter wheel as the wheel is pulled or pushed through the V-shaped section. This type of machine often experiences high levels of lateral and vertical vibration due to the bucking reaction of the cutter wheel on the uneven stump profile. The result of such uneven loading and high vibration can be particularly harsh on the transmission of a tractor with a power take-off (PTO), from which many stump grinders are driven.
It is also known to mount stump cutter teeth on one or both faces of a cutter wheel which is swung from side to side during a cutting operation with the teeth on one face or the other contacting and grinding a stump from the side. Examples of this type of equipment are described in the following patents:
______________________________________ Patent No. Inventor Issue Date ______________________________________ RE 28,651 Welborn Dec. 16, 1975 3,732,905 Pickel May 15, 1978 4,271,879 Shivers et al. Jun. 9, 1981 4,709,736 Bellars Dec. 1, 1987 4,848,423 Yoder Jul. 18, 1989 ______________________________________
This type of machine ordinarily requires its own engine for power, which adds to the expense of the machine, or, particularly, in the case of PTO-driven machines, a 90.degree. gearbox or a hydraulic drive, either of which is a costly item in relation to the other parts of a machine. Hydraulic drives are also less efficient than direct drives.
Stump grinders are also available with cutter teeth mounted on the periphery of a drum or wheel mounted so as to rotate vertically in a longitudinal direction, with the drum being moved vertically and/or longitudinally during a cutting operation, and in some cases with the lateral position of the drum being adjustable via a pivot mechanism. One such stump grinder, disclosed in U.S. Pat. No. 4,041,996 to Grover, is adapted for attachment to an excavator and is driven by a rotary hydraulic and/or electric motor coaxially mounted with a cutter drum. Alternatively, power to a drum with such a mounting configuration is known to be supplied via a 90.degree. gearbox, a relatively expensive item as pointed out above.
In spite of decades of activity in this area there remains a need for a relatively low-cost, reliable, easily operated, stable stump grinder capable of providing smooth yet relatively rapid cutting action.